This invention relates to short range wireless communications technologies, such as HomeRF, 802.11 FHSS, and Bluetooth(trademark), and specifically to a method and apparatus to provide a non-desensitizing, non-interfering dual transceiver device for use in such technologies.
Many wireless communication systems make use of spread spectrum technologies and operate in the unlicensed industrial, scientific and medical (ISM) band, as regulated by FCC part 15 rules. While all such systems are allowed to use the same frequency band, each has its own air interface, communication protocols, and applications. In the 2.4 GHz ISM band, there are many existing and emerging standards, e.g., 802.11 WLAN, Bluetooth(trademark) and HomeRF. Bluetooth(trademark) is a trademark/service mark of Telefonaktiebolaget LM Ericsson, of Stockholm, Sweden for telecommunication equipment, computer. communication equipment, including radio modems; and telecommunication and computer communication services.
802.11 WLAN products have been around for some time and are mostly used in an office infrastructure. Bluetooth(trademark) and HomeRF, on the other hand, address the needs of cordless cable replacement for portable devices and home networking, respectively. It is not difficult to envision two or more wireless systems co-existing in an office, in a residential area, or even public places. Given the foregoing scenarios, each product must operate in the presence of interference generated by other co-existing systems, and still perform properly. Moreover, it is also desirable from the user""s point of view to have only one wireless device, which may be used in various environments, rather than having to carry multiple wireless devices, and to have to change hardware and software configurations, depending on location and the presence of other ISM band devices.
Desensitization is a phenomenon wherein a receiver""s sensitivity degrades due to excessive signal strength, which may overload the front-end circuits of the radio. The receiver will be desensitized if there is a second radio operating in close proximity, particularly if the two radios do not transmit in synchronization with each other.
Attempts to solve the problem of dual mode operation in a single transceiver include (1) switching between the two modes, (2) time multiplexing different protocols of frequency bands, or (3) reserving a certain period of time in one mode to allow transmission in another mode. There is no known prior art which provides a solution for simultaneous dual mode operations in the shared spectrum using different transceivers in a single enclosure.
U.S. Pat. No. 5,390,345 to Wada et al. for Method for preventing desensitization and radio interference of radio receivers, granted Feb. 14, 1995, describes a method for using the level of cross modulation from the output of a high frequency amplifier, or mixer, as an indication of severe interference, and which controls the gain of the amplifier, or the attenuation of a variable attenuator preceding the amplifier, to avoid receiver desensitization.
U.S. Pat. No.5,392,300 to Borth et al., for Dual mode radio communication unit, granted Feb. 21, 1995, describes communication units which are capable of protecting data transmission with encoders/decoders in either error detection or forward error correction modes. A mode selector switch is used for selecting the desired mode of operation.
U.S. Pat. No. 5,630,224 to Swail, for Method and apparatus for avoiding desensitization of a radio frequency receiver, granted May 13, 1997, describes a techniques for avoiding receiver desensitization by changing the frequency being used by a subscriber unit or delaying the data transmission. The detection of interference is achieved by comparing measured BER (bit error rate) vs. expected BER, for RSSI (received signal strength indicator) of the same level.
U.S. Pat. No. 5,710,986 to Obayashi et al., for Dual mode radio communication apparatus having function of selectively designating analog or digital mode, granted Jan. 20, 1998, describes use of a mode designation switch selectively designating analog mode or digital mode.
U.S. Pat. No. 5,765,113 to Russo et al., also entitled Method and apparatus for avoiding desensitization of a radio frequency receiver, granted Jun. 9, 1998, describes techniques for avoiding receiver desensitization.
U.S. Pat. No. 5,884,189 to Yamazaki et al. for Multiple-modes adaptable radiotelephone, granted Mar. 16, 1999 describes a radiotelephone which uses a single wireless transceiver for modulating and demodulating signals in the transmitting/receiving frequency bands for both a cellular telephone system (AMPS) and a cordless telephone system (ISM band). A control unit, which incorporates the software for TIA/EIA/IS-94, is provided to control the wireless transceiver.
The specification of Bluetooth System, Version 1.0 B, December 1999, may be found at bluetooth.com. The specification for HomeRF Shared Wireless Access Protocol(SWAP-CA) Specification Revision 1.2, October. 1999, may be found at http://www.homerf.org.
A dual mode RF radio includes a first transceiver operating under a first transmitter/receiver protocol, and having a first receiver portion and a first transmitter portion therein; and a second transceiver operating under a second transmitter/receiver protocol, and having a second receiver portion and a second transmitter portion therein; wherein both transmitter/receiver protocols are spread spectrum protocols; a shared antenna operatively connected to both said first transceiver and said second transceiver; and an isolation mechanism for isolating said first and second receiver portions from a transmitter portion while said transmitter portion is transmitting, including a circulator for connecting said receivers and said transmitters to said antenna, a power splitter for splitting a received signal between said first transceiver and said second transceiver, and a power, combiner for combining a transmitted signal from said first transceiver and said second transceiver.
A method of simultaneously operating a dual mode RF radio includes operating a first transceiver under a first transmitter/receiver protocol; operating a second transceiver under a second transmitter/receiver protocol, wherein both transmitter/receiver protocols are spread spectrum protocols; sharing an antenna between the first transceiver and the second transceiver; and isolating the receiver portions of the transceivers from the transmitter portion of the transceivers while a transmitter portion is transmitting, including providing a circulator for connecting the receiver portions and the transmitter portions to the shared antenna.
An object of the invention is to provide a single device which is capable of simultaneous dual mode operations in the same shared frequency spectrum.
Another object of the invention is to provide multiple services for users of different systems.
A further object of the invention is to provide an apparatus and method wherein frequency selection in one system may be used by the other system through a shared backend processor.